1. Field of the Invention
The present invention generally relates to a semiconductor device, a method for producing thereof and a lead frame used therein, and more particularly to a semiconductor device in which a strength of a lead frame and a heat release efficiency can be improved, a method for producing thereof and a lead frame used therein.
2. Description of the Prior Art
Currently, in order to respond to a demand for a high-performance semiconductor device, a number of pins provided in a QFP (Quad Flat Package) type semiconductor has been increased. With this trend, an inner lead in a lead frame used in the semiconductor device becomes thinner and the strength thereof is lowered. Also, a heat amount generated by a semiconductor chip is increased. Therefore, the strength of the lead frame and the heat release efficiency of the semiconductor chip are required to be improved.
FIGS. 1A, 1B and 1C are sectional views showing conventional multi-pin type semiconductor devices.
In general, as a semiconductor device including a semiconductor chip is required to be decreased in size to meet the demand for the high-performance semiconductor device, the number of pins is increased and a pitch of pads formed in the semiconductor chip is decreased. Accordingly, ends of inner leads to be bonded to the pads via wires become fine, and a small-size pitch is required thereof.
However, when a lead frame of, for example, 0.15 mm in thickness is produced, an etching for making the ends of the inner leads with a small pitch is limited in accuracy, and the ends of the inner leads cannot be positioned close to a position at which the semiconductor chip is mounted.
In a semiconductor device 11 shown in FIG. 1A, after a thickness of an end portion 13a of an inner lead 13 of a lead frame 12 is made a half of the original by a half-etching process, the end portion is patterned to the small-size pitch by an etching process.
The semiconductor device 11 is disclosed in Japanese Laid-Open Patent Application No. 59-98547. In the semiconductor device 11, a film 15 is attached to the above-mentioned inner lead (end portion 13a). Between the inner leads 13 facing each other on the film 15, a semiconductor chip 16 is mounted through an adhesive 17. After the end portions 13a of the inner leads 13 are bonded to pads provided in the semiconductor chip 16 through wires 18, a package 19 is formed by a resin molding. Outer leads 14 extending from the package 19 are formed in a gull-wing shape for a surface connection.
On the other hand, a semiconductor device 21 shown in FIG. 1B is disclosed in Japanese Laid-Open Patent Application No. 4-6863. In this semiconductor device 21, an end portion 23a of an inner lead 23 in a lead frame 22 is apart from a semiconductor chip 25 in order that a plurality of pins can be provided in the semiconductor device 21. In this case, a heat spreader 26 on which the end portions 23a of the inner leads 23 are secured is used in order to improve a heat release efficiency. On the heat spreader 26, the semiconductor chip 25 is mounted through an adhesive 27. Pads provided on the semiconductor chip 25 are connected to the end portions 23a of the inner leads 23 through wires 28. A package 29 is formed by a resin molding and outer leads 24 extending from the package 29 are formed in the gull-wing shape.
In a semiconductor device 21A shown in FIG. 1C, on the heat spreader 26 shown in FIG. 1B, patterns 26a connected to corresponding inner leads 23 are formed. The pads in the semiconductor chip 25 are bonded to the patterns 26a through wires 28a. These wires 28a can be shorter than the wires 28 and a cost for wires can be reduced accordingly.
However, in the semiconductor device 11 shown in FIG. 1A, though the thin end portions 13a of the inner leads 13 are reinforced by the film 15, the end portions 13a are not strong enough. That is, the end portions 13a may be changed in shape when the molding resin is molded at a high pressure, and a reliability of the semiconductor device 11 may be lowered.
Also, in the semiconductor device 21 shown in FIG. 1B, though a multi-pin type semiconductor device is available without making the inner leads 23 thinner, the end portions 23a cannot be positioned close to the semiconductor chip 25 and the wires 28 become longer. It increases the cost for wires and prevents a high-speed operation of the semiconductor device.
Further, in the semiconductor device 21A shown in FIG. 1C, though the wires 28a are shorter, the cost is increased by forming the patterns 26a on the heat spreader 26.